The color effect and gamut of liquid crystal display (LCD) TV is getting more and more attention currently. The wide color gamut has become a new development tendency for TV backlight. Color gamut is quantitatively measured by NTSC. Higher NTSC shows better ability of color display. Each pixel of LCD TV consists of three color (R, G and B) rectangular blocks. The color display ability depends on the performance of back-light module and color filtering film. Cold cathode fluorescent lighting (CCFL) is normally used as back light for conventional TV module, in which NTSC is only 65% to 75%. LED as a new lighting source, which has advantages such as high reliability, energy saving, environmental protection, will gradually replace the traditional CCFL lighting. The NTSC performance can normally reach 72% to 80% when using blue LED+YAG phosphor. However, NTSC value can be achieved to 80% or more while using blue LED+Green/Red (G/R) phosphor. Full width at half maximum (FWHM) of G/R phosphor will affect the performance of NTSC. Generally the smaller FWHM of G/R phosphor will cause higher NTSC. If FWHM of G/R phosphor is achieved to less than 50 nm, the NTSC could be easy to reach 90%. However, FWHM is hard to be achieved to less than 50 nm for conventional Green phosphor and 70 nm for Red phosphor used in LED, which results in a limit of NTSC performance for LED package using conventional phosphor.
Currently it has become an important way to find a kind of phosphor with small FWHM to achieve the wide color gamut. For example, using nanometer-scaled material quantum dot (QD) and non-rare earth red phosphor K2SiF3/Mn, in which FWHM can reach less than 30 nm, the NTSC performance is easy to reach 95%, even more than 100%. However, these materials have strong toxicity, which would limit their application to a certain extent.
The FWHM of red or green LED chip is less than 40 nm. Compared with red/green phosphor, red/green LED chip has smaller FWHM. If the red/green LED chips are used in TV backlight, the NTSC performance is easy to reach more than 90%. The difficult point of this solution is how to adjust the ratio of different LED color chips to obtain a desired color coordinate point. Moreover, adding the red/green chips in TV back-light will result in cost increases.
Thus it become a technical barrier for the people in the art to find a method to reduce the stringent requirements of phosphor FWHM based on conventional phosphor converted package, so as to achieve much wider color gamut.